The present invention relates to improvements in municipal solid waste material sorting systems, and is more particularly concerned with sorting or classifying such waste whereby to facilitate recovery of various useful fractions thereof, including metals, glass and plastic containers.
Disposal of municipal solid waste material creates an enormous problem in most communities, and the larger the communities and the more dense the population, the larger the problem. In many communities landfill or dumping sites are becoming exhausted, and new landfill sites are often not conveniently available and are nearly always difficult, if not impossible, to find. Incineration or "mass burning" is frequently resorted to, but is unsatisfactory in many respects compared to processing or classifying of municipal solid waste to sort out useful fractions, as herein. Incineration requires large expenditures of energy, is usually a very wasteful manner of waste disposal, and often creates new disposal problems because incinerator ash contains materials which can require the ash to be classified as hazardous waste.
There have been numerous examples of prior classification systems according to which various sizes of the same material such as ore, coal and the like are graded. However, municipal waste because of its heterogenous nature presents special problems for the attainment of reasonable efficiency and acceptably economical methods and means for the separating of useful fractions from the large tonnages of municipal waste materials generated on a continuous basis.
Although municipal solid waste contains some materials for which there may be no immediate recyclable value and which must therefore go to landfill, a major percentage of municipal solid waste may be recovered and with economical separation contribute various valuable source materials such as, but not limited to, combustibles including paper, cardboard, certain plastics, wood, yard wastes, fabric, and the like; fibrous materials that can be recycled into roofing felt or new corrugated cardboard; recyclable materials such as plastic, glass and metal containers; miscellaneous metal scrap, and the like.
U.S. Pat. No. 4,044,695 discloses a fairly elaborate multi-stage pneumatic municipal solid waste separation and recovery system capable of handling very large volume, primarily for separation into combustible and noncombustible fractions.